Approximately 2-8% of infants younger than 3 years and about 2% of the adult population are affected by food hypersensitivities. About 80% of allergic reactions in children are the result of hypersensitivity to cow's milk (CM), hen's egg and legumes (e.g. peanuts and soybeans). In the adult population, however, allergy to fruits, peanuts and tree nuts represent the hypersensitivities with the highest prevalence.
Cow's milk is among the first foods introduced into an infant's diet and thus one of the most common causes of food allergy in young children. About 2.5% of neonates show adverse reactions to cow's milk in the first year of their life.
Symptoms of cow's milk allergy (CMA) are either of immediate or delayed type and they range from mild to severe reactions that involve the skin, the respiratory tract, gastrointestinal tract and in the worst case appear as life-threatening systemic reactions (anaphylaxis). In contrast to the cell-mediated delayed type reactions, immediate reactions are caused by the production of immunoglobulin E (IgE) antibodies in response to otherwise harmless antigens (Type I hypersensitivity). The interaction of IgE antibodies with the allergenic molecule leads to specific activation of effector cells (mast cells, basophil granulocytes) and to a subsequent release of inflammatory mediators like histamine, prostaglandine, and leukotriene which are responsible for the immediate-type allergic reactions.
Cow's milk contains more than 25 proteins and some of them are known to be allergenic. By the action of chymosin (rennin) or by acidification of milk to pH 4.6 two fractions are obtained: Twenty percent of the proteins are found in the whey fraction and 80% of proteins comprise the casein fraction. Allergenic molecules are contained in both fractions and considered either major or minor allergens depending on the incidence of documented allergic responses in the CMA population.
Major allergens present in cow's milk are alpha-lactalbumin, beta-lactoglobulin, alphaS1-casein, beta-casein and kappa-casein. Minor allergens present in cow's milk are alphaS2-casein, lactoferrin, bovine serum albumin and immunoglobulin.
Alpha-lactalbumin (Bos d 4), beta-lactoglobulin (Bos d 5), immunoglobulins (Bos d 7), BSA and lactoferrin are the well-known IgE-reactive components in whey. AlphaS1-casein, alphaS2-casein, beta-casein and kappa-casein are the potent allergens in the casein fraction (Bos d 8) (Wal, 2004).
In the whey fraction beta-lactoglobulin (BLG) and alpha-lactalbumin (ALA) are regarded as major allergens. Beta-lactoglobulin is a globular and very stable protein which belongs to the lipocalins, a protein superfamily, that bind hydrophobic ligands. Other allergens, like the major dog allergens Can f 1 and Can f 2 and allergens of other furred animals (horse, cat, and guinea pig) also belong to this protein superfamily. Beta-lactoglobulin naturally occurs in a dimeric form with a molecular weight of 36 kDa. There are two major isoforms of beta-lactoglobulin, the genetic variants A (BLGA) and B (BLGB), which differ in amino acids 64 and 118 (aspartic acid and valine in BLGA, glycine and alanine in BLGB). Stability and the fact that beta-lactoglobulin belongs to the family of lipocalins may explain the high allergenic potential of this molecule.
Alpha-lactalbumin is a 14 kDa acidic Ca2+ binding monomer stabilized by four disulfide bridges. It is a regulatory component in the galactosyltransferase system that synthesizes lactose. Sequence analysis showed high amino acid sequence homology to human alpha-lactalbumin (hALA) and lysozyme from hen's egg; a major allergen of hen's egg. The allergenicity of alpha-lactalbumin may be explained by its stability.
In suspension the proteins of the casein fraction form ordered aggregates (micelles) with a constant proportion of the individual molecules: alphaS1- and alphaS2-casein 37% each, beta- and kappa-casein 13% each. The four casein molecules have little primary structure homology, have different functional properties, but are all phosphorylated proteins with rheomorph, highly hydrated tertiary structures that can be easily degraded by some proteases. This sensitivity to proteolytic digestion is a rather unusual characteristic for an important allergen. Cow's milk caseins share amino acid sequence homologies of up to 90% with caseins of other mammals, like goat and sheep. This sequence homology might be the reason for the frequently observed cross-reactivity between cow's milk and milk from other animals.
The present disclosure addresses the need to provide methods which allow to identify allergenic proteins and peptides present in a biological source. The present disclosure thereby also addresses the need to provide methods which allow one to identify non-allergenic proteins and peptides present in a biological source, in particular in cow milk and nutritional formulations containing cow milk. Moreover, the disclosure provides methods for diagnosing and treating an allergy in an individual.